Dry weather, distance are barriers for Mexican ASR

With Asian soybean rust having been found in Mexican soybeans, Tom Isakeit has been on his toes.

“We’re monitoring sentinel plots scattered from Wesleco to north of Dallas,” says the busy Texas A&M plant pathologist. “There’s also a couple on the High Plains. As far as an alert system, the sentinel plots are our main focus.”

There are also spore traps in the state but Isakeit is less impressed with them. In mid-May, reports emerged that spores trapped in Fort Bend County were “like” those generated by ASR. But they were never positively identified.

“That’s a big consideration. I want to emphasize that spore traps can’t be relied upon to provide an early warning. Without enough spores to run a PCR or other tests to confirm identity, the trapped spores don’t tell us much. They could be rust spores from anything. Also, when dealing with these spore traps, we’re unsure if the spores are even alive. That points toward the importance of sentinel plots. Unfortunately, spore-trapping adds a lot of confusion to the situation.”

As late as May 20, Isakeit checked a kudzu patch northeast of Houston where he found ASR last year. He’s also been checking another patch north of Livingston and found nothing suspicious.

“I’m confident that ASR didn’t overwinter in that kudzu. It all died back and the rust died with it.”

Because of an ASR find on south Texas soybeans in February, Isakeit has been more concerned about Wesleco and the Lower Rio Grande Valley. But sentinel plots in the areas are clean.

“I traveled there last month to look at some commercial beans and again found nothing. There are some people checking edible legumes in the area and those crops are clean, as well.”

It’s been very dry recently, especially in south Texas. “When ASR mobility is talked about, people often say it has to move in ‘small steps’ – a few hundred miles or less. The dry weather we’re having would certainly help hold it off.

“Assuming there’s a source in Mexico, there’s not much in south Texas that’s susceptible to ASR. There is very small acreage of soybeans in the Lower Rio Grande Valley, maybe a few hundred acres. Spores can shower the crop but, unless there’s enough wetness for the right amount of time, nothing will happen.”

And there’s another large soybean gap between the Lower Rio Grande Valley acreage and the next large area of commercial soybeans in Victoria, south of Houston.

“Victoria has been pretty dry, as well. They’ve only been hit with small, isolated showers. That surely helps restrict disease development.”

For these reasons, “the spore trap report was a bit frustrating. I knew the weather conditions weren’t conducive to rust. I went out and personally verified that the sentinel plot (near the trap), along with three commercial fields nearby, had no ASR.”

How is the Mexican ASR situation being monitored?

“They don’t have an Extension system there like ours. There are some people down there that are supposed to be working with USDA. Thus far, most of the Mexican ASR information has come from Syngenta.”

In the past, Isakeit has done work in the Tampico area of Mexico where ASR has been found. That’s about a six-hour drive from the U.S. border.

And there is some precedence for worry. When Texas experienced sorghum ergot – a disease where spores can be windborne and sent north -- it was first found in that area of Mexico.

“We were able to track that disease on volunteer sorghum alongside roads. So I’m not saying, ‘Those ASR incidences in Mexico are so far away that we don’t need to worry.’ No, it’s something we need to look out for. But, right now, if spores are brought to us from Mexico, they probably won’t do much because it’s so dry.

“And we’re heading into the time of year when it becomes very hot. The commercial beans in south Texas will be finishing up in another month or so.”